Segment Information - Summary of Prior Period Financial Information Restated (Detail) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended	9 Months Ended
	Sep. 30, 2015	Jun. 30, 2015	Sep. 30, 2014	Jun. 30, 2015	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting Information [Line Items]
Net income (loss)	$ 280,401		$ 275,344		$ 808,702	$ 788,697
Business Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	23,995		25,038		74,160	73,763
Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	108,422		100,705		312,926	303,637
Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net income (loss)	85,312		78,676		250,501	230,254
Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net income (loss)	5,113		12,495		21,823	38,898
Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	21,150		22,749		75,462	64,680
Retail Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)	64,721		72,057		202,415	214,064
All Other [Member]
Segment Reporting Information [Line Items]
Net income (loss)	$ (28,312)		(36,376)		$ (128,585)	(136,599)
Net Income (Loss) as Previously Reported [Member]
Segment Reporting Information [Line Items]
Net income (loss)			275,344			788,697
Net Income (Loss) as Previously Reported [Member] | Business Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)			30,905			87,263
Net Income (Loss) as Previously Reported [Member] | Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)			101,740			306,863
Net Income (Loss) as Previously Reported [Member] | Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net income (loss)			78,581			230,668
Net Income (Loss) as Previously Reported [Member] | Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net income (loss)			8,279			34,538
Net Income (Loss) as Previously Reported [Member] | Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)			25,021			72,144
Net Income (Loss) as Previously Reported [Member] | Retail Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)			32,901			94,646
Net Income (Loss) as Previously Reported [Member] | All Other [Member]
Segment Reporting Information [Line Items]
Net income (loss)			(2,083)			(37,425)
Impact of Changes [Member]
Segment Reporting Information [Line Items]
Net income (loss)		$ 3,000		$ 5,000
Impact of Changes [Member] | Business Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)			(5,867)			(13,500)
Impact of Changes [Member] | Commercial Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)			(1,035)			(3,226)
Impact of Changes [Member] | Commercial Real Estate [Member]
Segment Reporting Information [Line Items]
Net income (loss)			95			(414)
Impact of Changes [Member] | Discretionary Portfolio [Member]
Segment Reporting Information [Line Items]
Net income (loss)			4,216			4,360
Impact of Changes [Member] | Residential Mortgage Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)			(2,272)			(7,464)
Impact of Changes [Member] | Retail Banking [Member]
Segment Reporting Information [Line Items]
Net income (loss)			39,156			119,418
Impact of Changes [Member] | All Other [Member]
Segment Reporting Information [Line Items]
Net income (loss)			$ (34,293)			$ (99,174)